Flat panel light source for a transillumination device of a microscope

ABSTRACT

A flat panel light source ( 100 ) for a transillumination device of a microscope comprises a plate-shaped light guide ( 110 ) having a lower and an upper boundary surface, and at least one lateral surface ( 113  to  116 ), and having at least one light-emitting means ( 120, 122 ) arranged to radiate light into the light guide ( 110 ) from at least two different directions, via at least one lateral surface serving as a light entrance surface, such that the light propagates in the light guide ( 110 ) as a result of total reflection, the total reflection being disrupted in defined fashion, by an element ( 140 ) abutting against a contact surface at the lower boundary surface of the light guide ( 110 ), so that an outcoupling of light occurs on the upper boundary surface of the light guide ( 110 ), the planar area of the contact surface being smaller than the planar area of the lower boundary surface.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims priority of German patent application number 102011 003 568.0 filed Feb. 3, 2011, the entire disclosure of which isincorporated by reference herein.

FIELD OF THE INVENTION

The present invention relates to a flat panel light source for atransillumination device of a microscope, in particular for those havinga continuously modifiable magnification, called “zoom microscopes” forshort, in particular stereomicroscopes or macroscopes.

BACKGROUND OF THE INVENTION

Flat panel light sources for a transillumination device of a microscopeare known from the existing art, for example from DE 10 2004 017 694 B3or US 7,554,727 B2. They are arranged below the specimen plane. Thedistance between the flat panel light source and specimen is selected tobe large enough that the specimen is completely illuminated, and thestructure of the light-emitting means is no longer visible in thespecimen plane. In the existing art, however, the overall height of thetransillumination base is too high. Ergonomic considerations are nottaken into account. In order to allow implementation of a flattransillumination device for microscopes, for example stereomicroscopesand macroscopes, a desire exists to configure the core element—the lightsource—to be as flat as possible but to radiate light homogeneously. DE10 2004 017 694 B3, for example, teaches the use of a diffusion diskover the light source for homogenization, although this has a negativeeffect on overall height and on the efficiency of the light-emittingmeans.

It is therefore desirable to describe a maximally flat but neverthelesshomogeneous transillumination device for a microscope.

SUMMARY OF THE INVENTION

According to the present invention, a flat panel light source for atransillumination device of a microscope is presented.

The invention is notable for the fact that light propagating in aplate-shaped light guide as a result of total reflection is outcoupledby deliberate disruption of the total reflection. The disruption occursat a lower boundary surface (“lower side”) of the light guide by way ofan element abutting against a so-called “contact surface.” As aconsequence, light is outcoupled at an upper boundary surface (“upperside”). The element is optically coupled to the light guide and isembodied so that diffuse scattering is produced, so that outcoupling oflight at the upper side occurs.

The contact surface contacted by the element acts as a radiatingsurface. The use of a light guide that, for outcoupling, is equippedonly with one contact surface not only makes it possible to obtain aparticularly flat conformation, but also results in an initialhomogenization of the radiated light because of the intermixing of lightinside the light guide.

A further homogenization is achieved by the fact that light is coupledinto the light guide from at least two different directions. In the caseof a light guide shaped like a prism or a truncated pyramid, forexample, i.e. a light guide having a polygonal base surface, incouplingoccurs at at least two of the lateral surfaces. In the case of acylindrical or frustoconical light guide, i.e. a light guide having anelliptical base surface, incoupling occurs at at least two locations onthe enveloping surface that are preferably distributed evenly over thecircumference. Incoupling from the side moreover allows a low overallheight.

A further improvement in homogenization is achieved by the fact that theplanar area of the contact surface is smaller than the planar area ofthe lower side. An edge region that serves not for radiation, butinstead exclusively for homogenization, therefore remains. The lightguide can therefore be selected to be as large as seems necessary forreasons of homogeneity, while the size of the contact surface (whichdefines the radiating surface) can be selected independently thereof

With the invention it is possible to create a flat panel light sourcefor a transillumination device of a microscope that radiates lightparticularly homogeneously. The flat panel light source is very flat inconformation and moreover is easy to manufacture and to handle.Manufacture is economical because expensive optics, and expensivealignment, are not necessary.

The configuration according to the present invention causes heatgeneration to be separated from the location where the light emission isused. This separation enables largely temperature-neutral illuminationof the sample. This arrangement proves advantageous specifically forimplementation of a large-area light source, since the necessary lightoutput of the light-emitting means increases as the square of thediameter of the emitting surface. Positioning of the radiating surfacebelow the sample therefore does not necessarily result in heating of thesample, since the heat-generating light-emitting means are arrangedlaterally, remotely from the sample. With the arrangement according tothe present invention, the heat that is produced can be betterdissipated.

Advantageous embodiments are the subject matter of the dependent claimsand of the description that follows.

The light guide is flat, so that its height is less than its lateralextension, in particular at least ten times less. As a result, thenecessary overall height is kept low, and the object plane, which islocated above the flat panel light source, does not migrate too farupward.

The element that disrupts total reflection preferably is reversiblydeformable. As a result, the planar area of the contact surface can bereversibly modified by a user so that the size of the contact surface,and thus of the radiating surface, can be defined and adjustedparticularly easily. The illumination device can thus be adapted to thatportion of the sample which is to be observed.

Particularly homogeneous radiating characteristics are achieved if theelement that disrupts total reflection produces a diffuse scattering ofthe light propagating in the light guide. The radiation thereby producedsubstantially obeys Lambert's law, so that the radiation density issubstantially constant in all directions. An ideally diffuselyscattering surface (according to Lambert's law) re-emits the irradiatedpower level in distributed Lambert fashion regardless of illuminationdirection, i.e. it appears equally bright regardless of the viewingangle (constant luminance). The element that disrupts total reflectionpreferably has a reflectance factor adapted to the at least onelight-emitting means.

The element that disrupts total reflection preferably has a reflectancefactor R of between 0.3 and 0.7. This is particularly suitable for notgenerating dazzle effects for the user when the light-emitting means arerelatively strong. On the other hand, a reflectance factor R of between0.7 and 1, in particular more than 0.7 or more than 0.9, is alsoparticularly preferred for weaker light-emitting means. These weakerlight-emitting means may exhibit a heat evolution that is advantageousbecause it is low. This allows a shorter distance between thelight-emitting means and the radiating surface, and thus a compactconformation for the flat panel light source as a whole.

The element that disrupts total reflection is preferably a liningapplied onto the lower boundary surface, in particular in the form of anapplied coating or film. The lining can be bonded on, painted on, spreadon, or the like. The lining is preferably embodied in the form of apaste that is to be applied. The paste usefully is light in color, e.g.white or beige, and usefully contains a large number of reflectingand/or scattering centers, for example embedded molecules.

The at least one light-emitting means usefully encompasses an LED or acold-cathode tube. The configuration of the light-emitting means has aparticular influence in terms of optimizing the light output transportedin the light guide. The radiating angle of the light-emitting means ispreferably adapted to the geometry of the light guide, efficiency beinginfluenced the height of the light guide, and by the distance betweenthe light-emitting element (e.g. chip) in the light-emitting means andthe light entrance surface.

An adaptation of the spacing of the light-emitting elements from oneanother helps to optimize homogeneity and to minimize the dimension ofthe light guide. A superposition of the incoupled light of adjacentsources takes place only starting at a certain distance from the edge ofthe light guide, which in turn depends on the aforesaid spacing of thelight sources. The planar area of the contact surface is therefore,according to the present invention, smaller than the planar area of thelower side, so that intermixing is achieved.

In a particularly preferred configuration, the plate-shaped light guideis embodied as a prism or as a truncated pyramid, i.e. the base surfacedefining the upper and the lower side is a polygon. With this type ofconfiguration, two or more lateral surfaces can each be particularlyeasily equipped with a light-emitting means. The manufacture andhandling of such a shape are moreover not associated with anydifficulties. It is furthermore particularly easy to provide coolingdevices (heat sinks, etc.) on the flat lateral surfaces in order to coolthe light-emitting means.

In a configuration that is also preferred, the plate-shaped light guideis embodied as a cylinder or a truncated cone, i.e. the base surfacedefining the upper side and lower side is an ellipse (including acircle). With this type of configuration, particularly goodhomogenization can be achieved if one or more light-emitting means arearranged on the circumference of the cylinder in such a way that“all-around” irradiation occurs.

The geometry and orientation, relative to the main beam proceeding fromthe light-emitting means, of the lateral surfaces of the light guidethat serve as light entrance surfaces can be used as a parameter forcontrolling the distribution of the light in the light guide and therebyfor influencing the homogeneity of the light radiated from the flatpanel light source. A tilting of the lateral surface serving as anentrance surface is mentioned here, for example. This modification ofthe entrance surface contributes to optimization of the overall heightof the flat panel light source, since with this action, regions of theelement that disrupts total reflection that are located closer to theoptical axis of the microscope experience better illumination coverage.

At least one entrance surface is preferably frosted. This homogenizesthe light distribution over the solid angle in the light guide. Largerangles in the light guide are thereby more heavily weighted, and thelight intensity is manipulated in favor of the edge zones of the elementthat disrupts total reflection.

It is a matter of course to deliberately define the optical refractiveindex of the element that disrupts total reflection. The light of thelight-emitting means is coupled laterally into the light guide andtransported by total reflection in the light guide until it isoutcoupled upward out of the plate by means of a controlled disruptionof total reflection (element that disrupts total reflection). Uponentering from air into the light guide having a refractive index n1,light is refracted toward the axis. It is then either totally reflectedor outcoupled at the outer sides. The equation governing the acceptanceangle a, which describes the maximum angle at which light can beincident onto the light guide so that it is still guided, is:

sin²(α)=n1² −n2²,

in which it is assumed that incoupling into the light guide occursthrough air (n=1). n2 is a possible refractive index of an adjacentmedium. For the case in which the adjacent medium is air (n2=1), theacceptance angle a encompasses the entire half-space as soon as therefractive index of the plate is selected as n1>✓2≈1.41. Predefinitionof the refractive index of the element that disrupts total reflection asn2 >1 causes outcoupling of that portion of the angular region for whichthe condition sin²(α)≧n1²−n2² is met. In a preferred embodiment, n2≧n1,so that all the light is outcoupled and scattered. This serves toincrease the luminance.

A diaphragm for defining a radiating surface is usefully provided on theupper side. If the diaphragm is additionally mirror-coated on the sidefacing toward the upper boundary surface, that light component is notlost.

Further advantages and embodiments of the invention are evident from thedescription and the appended drawings.

It is understood that the features recited above and those yet to beexplained below can be used not only in the respective combinationindicated, but also in other combinations or in isolation, withoutleaving the context of the present invention.

DESCRIPTION OF THE FIGURES

The invention is schematically depicted in the drawings on the basis ofan exemplifying embodiment, and will be described in detail below withreference to the drawings.

FIG. 1 a is a plan view of a first preferred embodiment of a flat panellight source according to the present invention.

FIG. 1 b is a cross-sectional view of the flat panel light source inaccordance with FIG. 1 a.

FIGS. 2 a and 2 b are plan views of further preferred embodiments offlat panel light sources according to the present invention.

FIG. 3 a is a cross-sectional view of a further preferred embodiment ofa flat panel light source according to the present invention in whichthe element that disrupts total reflection assumes a first shape.

FIG. 3 b shows the embodiment according to FIG. 3 a, the element thatdisrupts total reflection assuming a second shape.

DETAILED DESCRIPTION OF THE INVENTION

In FIGS. 1 to 3, identical elements are labeled with identical referencecharacters.

FIGS. 1 a and 1 b, which depict a first preferred embodiment of a flatpanel light source respectively in a plan view and a cross-sectionalview, will be described below in continuous and overlapping fashion.

In FIG. 1, a first preferred embodiment of a flat panel light sourceaccording to the present invention for a transillumination device of amicroscope is depicted schematically in a plan view and labeled in itsentirety with the number 100.

Flat panel light source 100 comprises a plate-shaped light guide 110.The plate-shaped light guide is made, for example, of acrylic, glass, orthe like and here has the shape of a prism, specifically a cuboid.Plate-shaped light guide 110 encompasses a lower (in this case, square)boundary surface 111 and a congruent upper boundary surface 112. Lightguide 110 has a lateral extension L and a height h, such that preferablyh<0.1 L.

Light guide 110 furthermore comprises four side surfaces 113 to 116. Inthe present example, light-emitting means 120 are coupled onto all sidesurfaces 113 to 116. Light-emitting means 120 encompass a carrier 121,serving simultaneously as a heat sink, on which are arranged a number oflight-emitting elements embodied here as light-emitting diodes 122.Light-emitting diodes 122 are arranged on light guide 110 in such a waythat light 130 radiated from light-emitting diodes 122 propagates in thelight guide as a result of total reflection. Light-emitting diodes 122are at a center-to-center distance s from one another.

Abutting against lower boundary surface 111 is an element 140 thatdisrupts total reflection and is embodied in the present example incircular fashion. Be it noted that a rectangular configuration is alsopreferred. The abutting region is referred to as a “contact surface” andhas a planar area A that is smaller than planar area L² of lowerboundary surface 111. In particular, the contact surface is at adistance 2 r from the lateral surfaces serving as entrance surfaces,which distance is preferably determined as follows:

In the light guide, the incoupled light is refracted by the refractiveindex n toward the vertical. A superposition of the incoupled light ofadjacent light-emitting diodes thus takes place only starting at adistance r=s/2*✓(n²−1) from the edge of the light guide. It is thereforeadvantageous to provide a total-reflection region at the edge of theplate so that good intermixing is achieved. Because of the non-isotropicangular characteristic of the light-emitting means, a width of at least2 r is typically provided for the edge zone.

The cuboidal shape of light guide 110 makes possible particularly simplehandling and attachment of light-emitting means 120, since lateralsurfaces 113 to 116 are flat.

In the present example, irradiation of light 130 occurs at all fourlateral surfaces 113 to 116, so that for purposes of the invention anirradiation of light occurs from four different directions. Although ina technical sense each of the individual light-emitting diodes 122radiates in infinitely many directions, “irradiation from differentdirections” is to be understood for purposes of the invention to meanthat the principal radiating directions of the light-emitting means aredifferent.

Element 140 that disrupts total reflection is usefully embodied as apaste applied onto lower boundary surface 111. A bonded-on film islikewise a possibility. Element 140 usefully is substantially opaque, sothat the majority of the incident light is not transmitted but insteadis scattered and is not lost. The reflectance factor is preferably above0.9. Element 140 is light in color, e.g. white or beige, and acts as adiffuse scattering surface. The result is that light 130 incident ontoelement 140 is diffusely reflected or scattered upward, such that aportion leaves light guide 110 at upper boundary surface 112 and can beused for transillumination of a sample 1 arranged thereabove.

A diaphragm, configured here as an aperture 150, is provided above upperboundary surface 112. The side of diaphragm 150 facing toward upperboundary surface 112 is mirror-coated.

In FIG. 2 a, a second preferred embodiment of a flat panel light sourceaccording to the present invention is depicted in a plan view andlabeled with the number 200. Flat panel light source 200 comprises acylindrical light guide 210 that is surrounded by a number oflight-emitting means 220 comprising light-emitting diodes 122. Paste 140is likewise applied on the lower side of the cylindrical light guide210.

The cylindrical shape of light guide 210, and the irradiation of lightfrom all directions associated therewith, result in particularly goodhomogenization of the radiated light.

In FIG. 2 b, a third preferred embodiment of a flat panel light sourceaccording to the present invention is depicted in a plan view andlabeled with the number 300. Flat panel light source 300 once againencompasses a prism-shaped light guide 310 whose base surface is in theshape of a regular hexagon. In the present example, all six lateralsurfaces of light guide 310 are equipped with light-emitting means 120so that irradiation of light occurs from six directions. This embodimentoffers on the one hand particularly good homogenization due toirradiation from many directions, and on the other hand flat lateralsurfaces that allow the light-emitting means, and also mounts, heatsinks, etc., to be attached easily.

FIGS. 3 a and 3 b depict a fourth preferred embodiment of a flat panellight source 400 according to the present invention in a cross-sectionalview. In contrast to flat panel light source 100 according to FIG. 1,flat panel light source 400 comprises an elastically deformable element440 to disrupt total reflection. Element 440 can be made, for example,of elastic plastic, such that the size of contact surface A can bemodified by deformation of element 440. The element can be embodied, forexample, in balloon-like fashion, deformation being possible byinflation and deflation. The element can also, for example, be embodiedresiliently, so that a deformation occurs as a result of appliedpressure (see FIG. 3 b) and release (see FIG. 3 a). The size of contactsurface A, and thus the size of the radiating surface, can be adjustedin this fashion to the size of sample 1 that is to be transilluminated.

1. A flat panel light source (100; 200; 300; 400) for atransillumination device of a microscope, for viewing a sample (1) inthe microscope, the flat panel light source (100; 200; 300; 400)comprising: a plate-shaped light guide (110; 210; 310) having a lowerboundary surface (111), an upper boundary surface (112), and at leastone lateral surface (113 to 116); at least one light-emitting means(120, 122) arranged to radiate light (130) into the light guide (110;210; 310) from at least two different directions, via at least onelateral surface of the light guide serving as a light entrance surface,wherein the light propagates in the light guide (110; 210; 310) as aresult of total reflection; and an element (140; 440) abutting against acontact surface at the lower boundary surface (111) of the light guide,wherein the element disrupts the total reflection such that anoutcoupling of light occurs through the upper boundary surface (112) ofthe light guide (110; 210; 310); wherein a planar area of the contactsurface is less than a planar area of the lower boundary surface (111).2. The flat panel light source (100; 200; 300; 400) according to claim1, wherein the element (140; 440) that disrupts total reflectionproduces a diffuse scattering, at the contact surface, of the light(130) propagating in the light guide (110; 210; 310).
 3. The flat panellight source (100; 200; 300; 400) according to claim 1, wherein theelement (140; 440) that disrupts total reflection is opaque and has areflectance factor R over the visible spectral region of 0.3≦R≦0.7 orR≧0.7 or R≧0.9.
 4. The flat panel light source (100; 200; 300; 400)according to claim 1, wherein the element that disrupts total reflectionis a lining applied onto the lower boundary surface (111).
 5. The flatpanel light source (100; 200; 300; 400) according to claim 1, whereinthe element that disrupts total reflection is a paste applied onto thelower boundary surface (111).
 6. The flat panel light source (100; 200;300; 400) according to claim 1, wherein the element that disrupts totalreflection is a film adhering onto the lower boundary surface (111). 7.The flat panel light source (100; 200; 300; 400) according to claim 1,wherein the element that disrupts total reflection is reversiblydeformable for varying the planar area of the contact surface.
 8. Theflat panel light source (100; 200; 300; 400) according to claim 1,wherein the optical refractive index of the element (140; 440) thatdisrupts total reflection is equal to or greater than the opticalrefractive index of the light guide (110; 210; 310).
 9. The flat panellight source (100; 200; 300; 400) according to claim 1, wherein the atleast one light-emitting means (120) comprises an LED (122) or acold-cathode tube.
 10. The flat panel light source (100; 200; 300; 400)according to claim 1, wherein at least one lateral surface of the lightguide that serves as a light entrance surface encloses, with the lowerboundary surface (111) and/or with the upper boundary surface (112), anangle that is less than or greater than 90°.
 11. The flat panel lightsource (100; 200; 300; 400) according to claim 10, wherein the angle isless than 85° or greater than 95°.
 12. The flat panel light source (100;200; 300; 400) according to claim 1, wherein at least one lateralsurface of the light guide that serves as a light entrance surface is atleast partly frosted.
 13. The flat panel light source (100; 200; 300;400) according to claim 1, wherein the plate-shaped light guide has theshape of a prism (110; 310), a truncated pyramid, a cylinder (210), or atruncated cone.
 14. The flat panel light source (100; 200; 300; 400)according to claim 1, further comprising a diaphragm (150) providedabove the upper boundary surface (112) for delimiting the light-emittingsurface.
 15. The flat panel light source (100; 200; 300; 400) accordingto claim 14, wherein the diaphragm (150) is mirror-coated on a sidethereof facing toward the upper boundary surface (112).